1. Field of the Invention
The present invention relates to a semiconductor device and a method of manufacturing a semiconductor device. In particular, the invention relates to a semiconductor device in which an electrode of a semiconductor element is joined to a joined member.
2. Description of Related Art
Japanese Patent Application Publication No. 2007-67158 (JP 2007-67158 A) discloses a semiconductor device in which a semiconductor element is joined to a joined member. In JP 2007-67158 A, the semiconductor element is joined to the joined member, on which a nickel layer is formed, through a Sn—Cu solder (mixed alloy solder of tin and copper). The proportion of Cu contained in the Sn—Cu solder is adjusted to be 3.0 wt % to 7.0 wt % (percent by weight). That is, the semiconductor element is joined to the joined member through a Sn-3.0 to 7.0Cu solder. JP 2007-67158 A describes that, when molten solder is solidified, a Cu6Sn5 compound is formed on a surface of the nickel layer. The Cu6Sn5 compound prevents mutual diffusion between nickel of the nickel layer and Sn of the Sn—Cu solder.
As described in JP 2007-67158 A, when a Sn—Cu solder containing lower than 0.9 wt % of Cu is used, theoretically, a Cu6Sn5 compound is not formed. Therefore, JP 2007-67158 A describes that a semiconductor element is joined to a joined member through a Sn—Cu solder containing 0.9 wt % or higher of Cu. In the description, as described above, it is more preferable that the proportion of Cu in the Sn—Cu solder is adjusted to be 3.0 wt % to 7.0 wt %.